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CleologicaI Tecknus fxc Page 5 <br /> Groundwater Monitoring Report <br /> Project No 724 2 <br /> January 17,2003 <br />' significant plume does not exist below the water table The presence of TPH-G <br /> contamination in well MW-106 and MW-107 suggests that a submerged plume is being <br /> sourced by residual soil contamination beneath the present water table It is noted that the <br /> screened intervals of these wells (55-60 feet bgs) are placed near the elevation of the <br /> groundwater table in 1992 —approximately 54 feet bgs <br /> As indicated in Figure 9 — MW-2 TPH-G vs GW Elevation, with the exception of June 20, <br />' 1997, contaminant concentrations have been stable in down gradient well MW-2 <br /> Oxidation/Reduction Potential (ORP) measurements (Table 5) show that wells MW-4, MW- <br /> 5 and MW-6 have positive values The negative DRP values observed in the rest of the <br /> wells show that they are either within the core of the contamination plume or are in the <br /> reaction/depletion shadow down gradient of the plume <br /> 3.0 CONCLUSIONS & RECOMMENDATIONS <br />' The contamination plume as observed from these wells is stable and does not appear to be <br /> sourcing a significant off site plume In GTI's opinion, the levels of contamination present <br /> do not warrant an engineered clean up <br /> In their correspondence dated April 24, 2002, the San Joaquin County Environmental <br />' Health Department (SJC/EHD) directed the submittal of a work plan for additional lateral <br /> plume definition GTI prepared this work plan on June 27, 2002 On September 3, 2002, <br />' Mr Nuel Henderson of SJC/EHD issued a letter requesting modifications to the work plan <br /> On September 25, 2002, GTI submitted a letter modifying the June 27, 2002 work pian <br /> The modifications have been approved by SJC/EHD and the work will be scheduled <br />' pending cost pre-approval from the USTCFP The goal of the revised plan is to target <br /> certain sand horizons for disciete screen monitoring and determine if preferred paths of <br /> migration may have allowed elevated concentrations to be missed by the current well <br /> spacing <br />